1. Field of the Invention
The present invention relates to an image processing apparatus, a program, and a storage medium.
2. Description of the Related Art
With the recent developments of image input/output technologies, there is a growing demand for higher image resolution. Taking the digital camera as an example of an image input apparatus, the price of a high performance charge coupled device (CCD) that has 3 million or more pixels is decreasing and this device is therefore starting to be widely used even in products that are within a commercially popular price range. Higher resolution and price reduction can also be seen in the fields of image output apparatuses and image display apparatuses, where hard-copy technologies applied to printers such the laser printer and the ink jet printer, for example, as well as soft-copy technologies applied to displays such as the CRT and LCD, for example, are developing.
With the introduction of such high-performance low-priced image input/output products to the market, high resolution images are becoming increasingly popular. Thus, in the future, it is expected that high resolution images will be in demand for all kinds of applications.
Under such circumstances, demand for improved compression/decompression technologies to facilitate handling of high resolution images will undoubtedly be on the rise as well. Accordingly, image compression technologies that satisfy such demand have been developed in the conventional art. An example of such technologies is the so-called JPEG 2000 technology, which enables processing of a high resolution image by subdividing the image into small units upon compression so that a high quality image can be decoded from the reduced image despite the use of a high compression rate.
In the conventional art, a technique of scrambling the image data is widely used when image data are handled for commercial purposes, for example. A typical application of such a technique can be seen in the distribution of contents over the Internet. Specifically, in a setting under the Internet environment where contents are provided to a user apparatus that makes access to a content-providing site, in some cases, depending on the type of contents, a commercial value may be attributed to image data being provided as the contents. In such case, when the image data corresponding to the contents are sent to a user apparatus, the user may view the image data and distribute the data to others, and thereby, the commercial value of the contents may be lost. To prevent such a loss, the image data provided as the contents may be scrambled so that a user may be unable to view the image data.
In this aspect, there is a growing demand for a technique for scrambling image data compressed according to the JPEG 2000 format. For example, in the prior art, a technique is disclosed in Japanese Laid-Open Patent Publication No. 2001-218184 for scrambling image data of an entire image or an area corresponding to a region of interest (ROI) by applying a scramble transform on quantized and encoded sub-band or bit plane data obtained from a wavelet transform process, which is a characteristic feature of the JPEG 2000 format.
In the case where scrambling of image data is realized by applying a scramble transform on quantized and encoded sub-band or bit plane data obtained from a wavelet transform process according to the JPEG 2000 format, the scrambled image data have no trace of the original image, and the original image cannot be recognized from the scrambled image.
However, in some cases such as the above example of providing image data as contents to a user over the Internet, it is preferred that the original image be recognizable to some extent from the scrambled image. That is, according to the nature of the human psyche, the desire to view an image in its proper state becomes stronger in a case where the image can be recognized to a certain degree but not enough to enjoy the image, for example, compared to a case in which the image is totally undecipherable. Thus, a technique for scrambling image data is required in which the original image can be recognized to some extent from the scrambled image.